Irak4, also known as Interleukin-1 Receptor Associated Kinase-4, is a kinase that plays a crucial role in innate immune responses. It integrates signaling downstream of receptors at the interface between innate and adaptive immune responses, such as Toll-like receptors (TLRs), interleukin-1R (IL-1R), and IL-18R. Irak4 is essential for the activation of the E3 ubiquitin ligase TNF receptor-associated factor 6 (TRAF6) by both MYD88 and TIR domain-containing adaptor protein inducing IFN-β (TRIF) in the TLR4 response, thus integrating MYD88 and TRIF in TLR4 signaling [4]. It is also a pivotal enzyme in the Toll-like receptor (TLR)/MYD88 dependent signaling pathway, which activates the NF-κB pathway [5].

In pancreatic ductal adenocarcinoma (PDAC), conditional deletion of Irak4 in KPC (p48-Cre/TP53f/f/LSL-KRASG12D) mice abrogated NF-κB activity, several immunosuppressive factors, checkpoint ligands, and hyaluronan synthase 2, which drive T cell dysfunction. This led to decreased tumor desmoplasia and increased abundance and activity of infiltrative CD4+ and CD8+ T cells, suggesting Irak4 drives T cell dysfunction in PDAC [1]. In inflammatory skin diseases, IRAK4 inhibition in murine models dampened disease activity, and in human lesional psoriasis and atopic dermatitis biopsies, it reversed pathogenic molecular signatures [2]. In a phase 1 trial, a KT-474 (an IRAK4 degrader) achieved IRAK4 degradation in blood and normalization in overexpressed skin lesions of patients with hidradenitis suppurativa (HS) and atopic dermatitis (AD), along with reduction of disease-relevant inflammatory biomarkers and improvement in skin lesions and symptoms [3].

In conclusion, Irak4 is a central player in immune-related signaling pathways. Gene-knockout or conditional-knockout mouse models have revealed its role in promoting T cell dysfunction in PDAC, driving inflammatory processes in skin diseases, and being involved in the pathophysiology of HS and AD. Targeting Irak4 shows promise as a therapeutic strategy in these disease areas.